Conventionally, various retardation plates have been used for optical compensation in various liquid crystal displays. An example of the retardation plates is an optically-biaxial retardation plate, and it can be produced in general by any of various polymer-film stretching methods (see JP3(1991)-33719 A, for example) like roller tensile stretching, roller press stretching, and tenter transverse uniaxial stretching, or a method of providing anisotropy through biaxial stretching (see JP3(1991)-24502 A, for example). Additional examples include a retardation plate in which a uniaxially stretched polymer film having a positive optical anisotropy and a biaxially stretched polymer film having a negative optical anisotropy and whose in-plane retardation is small are used in combination (see JP4(1992)-194820 A, for example), and a retardation plate formed, not by the above-mentioned stretching, but by processing polyimide into a film on a substrate and thus provided with a negative uniaxiality derived from the nature of the polyimide itself (see JP8(1996)-511812 A, for example).
According to the above-mentioned film-stretching technique or the like, the thus formed stretched film can be provided with, for example, a negative biaxial optical property of nx>ny>nz. Here, nx, ny and nz indicate respectively refractive indices in directions of an X-axis, a Y-axis, and a Z-axis in the stretched film. The X-axis direction is a direction showing a maximum refractive index within the plane of the film, the Y-axis direction is a direction perpendicular to the X-axis direction within the plane, and the Z-axis direction is a thickness direction and is perpendicular to the X- and Y-axes directions. When arranged between a liquid crystal cell and a polarizer of a liquid crystal display, a retardation film having the above-stated optical property can widen a viewing angle of the liquid crystal display, and thus it is useful as a viewing angle compensating film for the liquid crystal cell.